linux-ext4 - [PATCH RFC 11/15] fanotify: Introduce filesystem specific data record

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Date:   Mon, 26 Apr 2021 14:41:57 -0400
From:   Gabriel Krisman Bertazi <krisman@...labora.com>
To:     amir73il@...il.com, tytso@....edu, djwong@...nel.org
Cc:     david@...morbit.com, jack@...e.com, dhowells@...hat.com,
        khazhy@...gle.com, linux-fsdevel@...r.kernel.org,
        linux-ext4@...r.kernel.org,
        Gabriel Krisman Bertazi <krisman@...labora.com>,
        kernel@...labora.com
Subject: [PATCH RFC 11/15] fanotify: Introduce filesystem specific data record

Allow a FS_ERROR_TYPE notification to send a filesystem provided blob
back to userspace.  This is useful for filesystems who want to provide
debug information for recovery tools.

Signed-off-by: Gabriel Krisman Bertazi <krisman@...labora.com>
---
 fs/notify/fanotify/fanotify_user.c | 27 +++++++++++++++++++++++++++
 include/uapi/linux/fanotify.h      | 10 ++++++++--
 2 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index cb79a4a8e6fb..e2f4599dfc25 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -69,6 +69,14 @@ static size_t fanotify_error_info_len(struct fanotify_error_event *fee)
 	return sizeof(struct fanotify_event_info_error);
 }
 
+static size_t fanotify_error_fsdata_len(struct fanotify_error_event *fee)
+{
+	if (!fee->fs_data_size)
+		return 0;
+
+	return sizeof(struct fanotify_event_info_fsdata) + fee->fs_data_size;
+}
+
 static size_t fanotify_location_info_len(const struct fanotify_event_location *loc)
 {
 	if (!loc->function)
@@ -295,6 +303,25 @@ static size_t copy_location_info_to_user(struct fanotify_event_location *locatio
 	return info.hdr.len;
 }
 
+static ssize_t copy_error_fsdata_info_to_user(struct fanotify_error_event *fee,
+					      char __user *buf, int count)
+{
+	struct fanotify_event_info_fsdata info;
+
+	info.hdr.info_type = FAN_EVENT_INFO_TYPE_FSDATA;
+	info.hdr.len = fanotify_error_fsdata_len(fee);
+
+	if (copy_to_user(buf, &info, sizeof(info)))
+		return -EFAULT;
+
+	buf += sizeof(info);
+
+	if (copy_to_user(buf, fee->fs_data, fee->fs_data_size))
+		return -EFAULT;
+
+	return info.hdr.len;
+}
+
 static int copy_info_to_user(__kernel_fsid_t *fsid, struct fanotify_fh *fh,
 			     int info_type, const char *name, size_t name_len,
 			     char __user *buf, size_t count)
diff --git a/include/uapi/linux/fanotify.h b/include/uapi/linux/fanotify.h
index 67217756dac9..49808c857ee1 100644
--- a/include/uapi/linux/fanotify.h
+++ b/include/uapi/linux/fanotify.h
@@ -124,8 +124,9 @@ struct fanotify_event_metadata {
 #define FAN_EVENT_INFO_TYPE_FID		1
 #define FAN_EVENT_INFO_TYPE_DFID_NAME	2
 #define FAN_EVENT_INFO_TYPE_DFID	3
-#define FAN_EVENT_INFO_TYPE_ERROR	4
-#define FAN_EVENT_INFO_TYPE_LOCATION	5
+#define FAN_EVENT_INFO_TYPE_LOCATION	4
+#define FAN_EVENT_INFO_TYPE_ERROR	5
+#define FAN_EVENT_INFO_TYPE_FSDATA	6
 
 /* Variable length info record following event metadata */
 struct fanotify_event_info_header {
@@ -166,6 +167,11 @@ struct fanotify_event_info_location {
 	char function[0];
 };
 
+struct fanotify_event_info_fsdata {
+	struct fanotify_event_info_header hdr;
+	char data[0];
+};
+
 struct fanotify_response {
 	__s32 fd;
 	__u32 response;
-- 
2.31.0